Wyse S10 not getting connected to Windows Server 2008 R2

Hi,
This problem is regarding Terminal Server connectivity (Remote Desktop Connectivity as per window server 2008). We have following working scenario :

Architechture : Client-Server
Server : Dell T430 PowerEdge
Server OS : Windows Server 2008 R2(Standard Edition)
Terminals : Wyse S10 thin clients firmware version 6.1.0_08, 6.5.0_22 and 6.5.0_40

Recently we've shifted to a new server DELL PowerEdge T430 from DELL PowerEdge 2900. The thin clients used to connect successfully to the old one. After the shifting process, the thin clients worked fine for about 1.5 months but suddenly today afternoon, they stopped connecting to the server all of a sudden.

Thanks in advance.